"Autocomplete" feature in Internet Explorers does not raise JavaScript events

I have an .ASP page that uses the onChange event to trigger a database lookup in the database. (After entering the code, the system checks the code and places a description next to it. IE GP1234 returns GP1234-Rubber Duck or GP1234-Invalid Code). The problem I am running into is that my users who have autocomplete are getting a list of previously used codes. If they use one of the codes in the list, data is entered, but no event is raised to direct the page to validate the data. I've tried OnChasnge, OnBlur and onMouseOut.
Any suggestions?